Quote:
Originally Posted by The HACK
The problem here isn't that the 1st and 2nd gear ratios are too different. Synchronizers will ensure that the next selected gear is spinning at the same speed as the output shaft. There are two possibilities as to why there's a 1st to 2nd gear grind:
1: The 1st/2nd synchronizer is shot.
2: The input shaft is not completely disengaged when shifting.
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While I agree with #2 (in fact on any other type of shift that's almost always the cause), but disregarding the wide ratio is incorrect, the collar is not completely blocked and if enough force is applied while not in sync the gear will grind.
More insight can be garnished from the fact that the grinding is actually very easily reproducible when shifting out of first in a high wheelspin situation of a burnout or drift where you're tires are moving quickly but the car is not. This effectively widens the gears even more by a pretty respectable amount.
It always amazes me how much the BMW community is numb to these sort of things which 90% of the the rest of the automotive community would quickly identify. I think it's the nature of the type which is an enthusiast who loves the car and driving, but doesn't work on their own car or get too much into the details.